In electrophotography, also known as Xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. The radiation selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image on the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The surface of the imaging member is then cleaned by a cleaning unit, such as a cleaning blade, to removal any residual marking particles before next printing cycle. The imaging process may be repeated many times with reusable imaging members. In order to maintain a clean surface for each print cycle, a cleaning unit, such as a cleaning blade may be incorporated.
Although excellent toner images may be obtained with multilayered belt or drum photoreceptors, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators, and printers are developed, there is a greater demand on print quality and useful life. Improved photoreceptor designs must target higher sensitivity, faster discharge, mechanical robustness, and ease cleaning. The delicate balance in charging image and bias potentials, and characteristics of the toner and/or developer must also be maintained. This places additional constraints on the quality of photoreceptor manufacturing, and thus on the manufacturing yield.
Imaging members are generally exposed to repetitive electrophotographic cycling, which subjects the exposed charged transport layer or alternative top layer thereof to mechanical abrasion, high friction with cleaning blade, and chemical attack from the charging device. This repetitive cycling leads to gradual deterioration in the mechanical and electrical characteristics of the exposed charge transport layer.
Providing a protective overcoat layer is a conventional means of extending the useful life of photoreceptors. An illustrative example of protective overcoats may include a cured composition formed from (i) a polyol binder, (ii) a melamine-formaldehyde curing agent; (iii) a hole transport material; (iv) an acid catalyst; and (v) a leveling agent coated from an alcoholic solution.
In conventional photoreceptors, mechanical wear due to cleaning blade contact or scratches due to carrier beads or contact with paper, causes photoreceptor devices to fail, and it may not be feasible to continue adding layers to improve photoreceptor robustness and therefore there is a need to develop new materials and systems that will respond and correct material breakdown as it occurs.
Despite the various approaches that have been taken for forming imagine members there remains a need for improved imaging member design, to provide improved imaging performance and longer lifetime, reduce its friction with cleaning blade, and minimize the frequency for maintenance, and the like.